[0001] The present invention relates to support pads for drill heads in particular for long
hole drilling in heat resistant steel materials. According to the invention the pads
are made of ceramic materials.
[0002] Drilling in metals is generally divided in two types: long hole drilling and short
hole drilling. Short hole drilling means generally drilling to a depth of up to 3-5
times the drill diameter. Long hole drilling means generally drilling to many more
times the drill diameter.
[0003] With short hole drilling the demands are not as great and therefore simple helix
drills either of solid cemented carbide or as solid tool steel or of tool steel equipped
with cemented carbide inserts are used.
[0004] Long hole drilling, however, puts large demands on good chipbreaking, lubrication,
cooling and not at least chip transport. This is achieved through specially developed
drilling systems with specially designed drill heads connected to a drill rod and
which fulfills the above mentioned requirements. The drilling head may be of solid
cemented carbide but is generally of tool steel or cast steel, provided with a number
of insert of cemented carbide placed in such a way that they together form the desired
cutting edge. Such long hole drills are known in the art.
[0005] The design of the long hole drilling head is such that the cutting forces are not
balanced. Therefore in order to absorb the resulting radial cutting forces the drilling
head is generally provided with support pads mechanically clamped to the head to support
and guide the head during the operation. Inserts and support pads are generally made
in cemented carbide with different contents of WC, Co and cubic carbides TiC, TaC,
NbC depending on the application. The support pads are, in addition, often coated
with one or more wear resistant layers. Generally the support pads are coated with
a yellow layer of TiN or WC/C+TiAlN.
[0006] However, when machining heat resistant superalloys such as Inconel 718,Inconel 939,
Waspaloy, Udimet 720 etc support pads in coated cemented carbide tend to become covered
with a network of small cracks which leads to rapid wear and too frequent change of
support pads.
[0007] In EP 0713747, the use of a coated ceramic guide member for a reamer is disclosed.
The coating is boron nitride or diamond. A similar reamer with a guide strip which
contains aluminum oxide and titanium carbide is disclosed in EP 0410342. Reamers are
used for finishing of pre-formed holes and are not subjected to the same type of forces
as drills for long hole drilling.
[0008] It is therefore an object to provide a support pad which is strong and durable particularly
when drilling in heat resistant materials.
[0009] FIG. 1 is a perspective view of an example of a drilling head provided with support
pads in which
1 - drilling head of the ejector type
2 and 3 - support pads
4 - central cutting insert
5 - intermediate cutting insert
6 - peripheral cutting insert
7 - internal cooling channel
[0010] As can be seen in Fig 1, the cutting inserts 4, 5 and 6 are clamped or brazed in
the drill head. The peripheral insert 6 forms the diameter of the hole in the workpiece
that is machined. The central insert 4 overlaps the central axis of the drill, as
no remaining core is desired. During rotation, the orbit of the cutting edge of the
intermediate insert 5 overlaps with the cutting edges of both the peripheral insert
5 and the intermediate insert 6 to thereby obtain a continuous cutting line from the
central axis to the periphery.
[0011] In the usual manner the drill head 1 is provided with an interior central channel
16, through which the major part of the chips are expelled.
[0012] According to the present invention there is provided a drill head with at least one
support pad of a ceramic material wherein the pad includes a base body with a bottom
surface, at least one side surface and a top surface. In a preferred embodiment the
support pad is 180° indexable.
[0013] In a first embodiment the ceramic material is essentially ceramic oxides or ceramic
oxides mixed with hard carbides and/or nitrides and/or borides and/or binder metal
and conventional pressing and/or sintering aids. In a preferred embodiment the ceramic
material is oxide based preferably consisting essentially of Al
2O
3 and/or ZrO
2.
[0014] In a second embodiment the ceramic material is nitride based containing conventional
pressing and/or sintering aids. In a preferred embodiment the nitride based material
consists essentially of Si
3N
4 and intergranular phase. In another preferred embodiment the ceramic material consists
of α- and/or β-sialon and intergranular phase.
[0015] In a third embodiment the ceramic material further contains whisker and/or platelets,
preferably of SiC.
[0016] The support pads according to the invention can be provided with a wear resistant
coating as known in the art.
[0017] The invention also relates to the use of a drill head provided with at least one
support pad of a ceramic material for drilling in heat resistant materials such as
Inconel 718, Inconel 939, Waspaloy, Udimet 720 etc.
1. Drill head comprising one or more support pads
characterized in that at least one support pad is made of a ceramic material.
2. Drill head according to claim 1 characterized in that said ceramic material is essentially ceramic oxides or ceramic oxides mixed with
hard carbides and/or nitrides and/or borides and/or binder metal and conventional
pressing and/or sintering aids.
3. Drill head according to claim 2 characterized in that said ceramic material is oxide based.
4. Drill head according to claim 3 characterized in that said ceramic material consists essentially of Al2O3 and/or Zr02.
5. Drill head according to claim 1 characterized in that said ceramic martial is nitride based containing conventional pressing and/or sintering
aids.
6. Drill head according to claim 5 characterized in that said nitride based material consists essentially of Si3N4.
7. Drill head according to claim 5 characterized in that said ceramic material consists of α- and/or β-sialon, intergranular phase.
8. Drill head according to any of the preceding claims
characterized in that said ceramic material further contains whisker and/or platelets, preferably of SiC.
9. Drill head according to any of the preceding claims
characterized in that said support pads are provided with a wear resistant coating.
10. Use of a drill head according to any of the preceding claims for drilling in heat
resistant materials such as Inconel 718, Inconel 939, Waspaloy, Udimet 720 etc.